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SAN BRUNO (CBS / AP) — Under fire for a deadly pipeline explosion in San Bruno, Pacific Gas & Electric Co. has revealed that its employees dispute key information the company gave federal investigators about past problems on the gas line that ruptured.

PG&E quietly released a document in May — more than eight months after the explosion killed eight people — showing that the same transmission line had sprung a leak a few miles away more than two decades earlier.

But the company revealed this week that its own workers’ accounts challenge the accuracy of that record given to the National Transportation Safety Board.

The conflicting reports about details of the 1988 leak are just the latest development in a long string of concerns about the company’s haphazard record-keeping in the wake of the September blast in San Bruno.

NTSB Chairwoman Deborah Hersman previously has chided the company for coming forward with critical information about the prior failure so long after the agency began its probe, saying it could hamper investigators’ progress.

In this week’s filing, PG&E revealed that none of the approximately 20 leak surveyors and pipe repairmen involved in the 1988 incident recalled a leak springing from a seam running lengthwise down the pipe, as the document given to NTSB in May states.

One worker said he remembered the leak stemming from a girth weld, a problem that also appeared in several other spots on the high-pressure line coursing through bedroom communities south of San Francisco, according to the filing.

Following the explosion, the California Public Utilities Commission ordered the company to hand over decades’ worth of safety records for its pipelines, and this week’s release includes more than 16,000 documents on welding problems.

NTSB investigators say last year’s blast originated at a poorly installed weld on the lengthwise seam of the transmission line, which PG&E previously believed was seamless.

Consumer advocates said shoddy accounting puts people at risk, and they wondered whether PG&E might reveal other erroneous records in the future.

“One day the records say one thing, the next day they say they say something else, the next day there are no records to be found or they were written in erasable ink,” said Mark Toney, executive director The Utility Reform Network, based in San Francisco. “The story keeps changing, and the more we learn, the more it sounds like there were repeated early warning signals on that line that were never followed up on.”

PG&E spokesman Brian Swanson initially said the small methane leak detected in 1988 was the result of a defect in a double-seamed weld running lengthwise down the transmission pipeline.

Swanson would not say earlier this week whether the company told federal investigators about employees’ conflicting accounts, but he subsequently clarified that the company notified NTSB about the new information at an undetermined “later” date. The NTSB declined to comment on the discrepancy, and CPUC spokeswoman Terrie Prosper said the commission only heard of the prior leaks as the information emerged through the NTSB’s investigation into the San Bruno blast.

“We have conflicting information,” Swanson said. “We’re learning valuable lessons from this investigation, and when all the facts are known about the cause of this terrible tragedy, we’ll be able to put in place the types of practices and procedures to help prevent this from happening again.”

The U.S. Department of Justice, as well as numerous state and local law enforcement and regulatory agencies, are pursuing their own investigations into what led up to the pipeline rupture.

Pipeline safety experts said it was concerning that PG&E lacked key details about weld flaws on the ruptured line, because girth weld and long seam weld leaks necessitate different kinds of safety tests.

The filing also provided new details on historical welding problems on the same high-pressure line: one in 2009 that prompted a leak in South San Francisco, and another in Sunnyvale in 1968.

“The reason you want to have well documented records is so you don’t have to ask people what they did last week much less in 1988,” said Washington state pipeline safety expert Richard Kuprewicz. “If they’re only now producing this information that could be very important to the NTSB, it puts everybody in a bad light.”

(Copyright 2011 by CBS San Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. Wire services may have contributed to this report.)